U.S. Pat. No. 2,387,065 describes a type of elastomeric mount. In this elastomeric mount a working chamber filled with fluid is subdivided by a partitioning membrane into two compartments and the partitioning membrane is connected by a rigid part, having a throttle orifice, with a support block and with a supporting elastomeric element. On compression of the mount downwardly, fluid which is pressurized in the lower compartment is bled through the throttle passage into the upper compartment. Good damping characteristics of the bearing are only obtained when the partition membrane is relatively stiff, so that during compresssion it does not yield to the increased pressure and force considerable damping liquid to flow through the throttle orifice.
When such a mount is used for supporting an internal-combustion engine in an automotive vehicle, good damping characteristics are only desired in the low-frequency oscillation range caused by road-surface unevennesses. For higher-frequency vibrations in the audible range the above-described mount retains its good damping and is, therefore, relatively hard, so that considerable sound from the engine is transmitted to the chassis and thence to the passenger compartment.
If the membrane is made relatively yieldable, damping for higher-frequency vibrations is reduced by deformation of the membrane as a result of the pressure differentials across it; then, however, in the lower-frequency road-caused vibration range the necessary damping is not obtained.